The present invention relates to a method of detecting an area of a document to be processed for an image forming apparatus and, more particularly, to a processing area detecting method which detects a marked area of a document so that image information existing therein may be extracted, erased, inverted as to black and white or otherwise processed.
Today, a digital copier, scanner input device, facsimile machine or similar image forming apparatus is extensively used. With a digital copier, for example, a person who does not want a part of image information printed on a document to be reproduced may copy the document after cutting off the part of interest or after covering it with a piece of white paper. This traditional scheme, however, has various problems left unsolved. Specifically, cutting off the needless part of a document is not only time-consuming but also impracticable without damaging the document. Covering the needless part by a piece of white paper is disadvantageous in that the white paper is apt to move to thereby prevent a plurality of copies from being provided with exactly the same appearance.
It has been customary, therefore, to mark a desired area of a document by use of a color felt pen or similar marker so that image information existing therein may be extracted, erased, inverted as to black and white or otherwise processed. However, when characters or similar image information printed on a document has the same density as the mark, the marked area cannot be detected with accuracy. Moreover, the mark is left on the document even after the latter has been copied. When the marked area is accurately detected, processing has to be executed to prevent the mark itself from being reproduced on a copy. This processing, however, brings about a problem that a part of image information of a document which has a relatively low density is not reproduced on a copy. Should such a part having a relatively low density be reproduced on a copy, the mark itself would be reproduced also. To eliminate such a dilematic situation, all the image information carried on a document may be copied, and image information on the resultant copy may be marked to specify a desired area. This, however, results in generation and, therefore, in the critical degradation of the quality of the output image.